beneath the table to the abstract. Use the Word Count cmd under Utilites menu for counting Significance HIV transmission to infants by breast feeding after maternally acquired anti-HIV antibodies decline is well documented. Neonatal vaccination may reduce HIV transmission to children in developing nations where safe alternatives to breast feeding are not available. However, a neonatal anti-HIV vaccine must elicit immunity in the presence of maternal HIV antibodies. Objectives Infection of newborn rhesus macaques with simian immunodeficiency virus is a well-established model for pediatric HIV infection and AIDS. This pilot study evaluated whether a live-attenuated SHIV-33 (virus from a molecular clone consisting of the HIV-1 SF-33 envelope gene in an otherwise SIV genome) could (1) establish infection in neonates with transplacentally acquired SIV antibodies, and (2) provide protection against oral SIV. Results Two rhesus macaques were immunized during pregnancy with whole-inactivated SIV in adjuvant. Both dams transferred high titer SIV-specific antibodies to their infants. Four neonates without SIV antibodies served as controls. All six infants were inoculated intravenously with SHIV-33 within 3 days of birth and all became infected. Virus levels remained low in all animals and none developed any clinical signs of disease by 24 weeks of age. Thus, maternal SIV antibodies did not prevent infection of neonates by a live vaccine. At one year of age SHIV-33-inoculated animals and 4 naove rhesus were challenged orally with pathogenic SIVmac239. All animals became infected after challenge; however, only animals inoculated with live-attenuated SHIV-33 had low viremia and no disease for >6 months. Controls had persistent, high viremia and 2 animals died with AIDS by 6 months after challenge. These results suggest that a live-attenuated HIV vaccine might be developed to protect in fants of HIV-infected women against oral exposure to HIV in breast milk. Future Directions Determine whether vaccinating newborn rhesus can provide protection against virulent SIV challenge within the first month of life. KEY WORDS pediatric simian AIDS, oral SIV transmission, perinatal HIV transmission, neonatal immunization, live-attenuated vaccine FUNDING NIH Grants RR00169 and AI039109, E. Glaser Pediatric AIDS Foundation Scientist Award 8-97